In an inkjet head of Patent Literature 1, as illustrated in FIG. 8, a plurality of nozzle holes is formed in matrix in a nozzle formation surface facing a recording surface of a recording medium so as to be arranged in a first direction parallel to a main-scanning direction orthogonal to a conveyance direction of the recording medium and in a second direction that is slightly inclined with respect to a sub-scanning direction serving as the conveyance direction of the recording medium.
In this inkjet head, nozzle holes n1 to n7 (defined to be a nozzle line N11) arranged in the second direction are located at a dot pitch P0 in the main-scanning direction, and the nozzle hole n7 on the most downstream side in the sub-scanning direction of the nozzle line N11 and a nozzle hole n8 on the most upstream side in the sub-scanning direction of an adjacent nozzle line N12 are also located at a pitch P2 equal to the dot pitch P0 in the main-scanning direction. Furthermore, the nozzle holes in the other nozzle lines N12, N13, N14, . . . are similarly located.
Although not illustrated, flow channels through which ink is supplied and driving mechanisms for ejecting ink are individually provided in a nozzle plate in which the nozzle holes are provided. When the nozzle holes are dispersedly located in the first and second directions as described above, location of the individual flow channels and the like is simplified while the dot pitch is reduced.
However, the above inkjet head is problematic in that, when inclination is generated in a direction of A1 or A2 in the figure due to a mounting error or the like of a body of the device, a change in the pitch P2 between the nozzle holes n7 and n8 tends to be larger than pitches between the other nozzle holes, and therefore light or shade is generated on a formed image along a line passing between the nozzle holes n7 and n8.
This problem arises because a pitch P4 in the sub-scanning direction between the nozzle hole n7 and the nozzle hole n8 is larger than a pitch P3 in the sub-scanning direction between other adjacent nozzle holes n1 to n7.
In order to solve the above problem, as illustrated in FIG. 9, in an inkjet head of Patent Literature 2, a nozzle hole n4 is located between a nozzle hole n7 and a nozzle hole n8 at a pitch P5 in a main-scanning direction and at a pitch P6 in a sub-scanning direction (P5=P2 (the pitch P2 in the main-scanning direction between the nozzle hole n7 and the nozzle hole n8 in FIG. 8), P6=P4/2).
With this, the pitch P6 in the sub-scanning direction between the nozzle holes n7 and n4 and the nozzle holes n4 and n8 which form adjacent dots can be formed to be a half of the pitch P4, and therefore an influence of a mounting error of the inkjet head can be reduced by half.